This study is a longitudinal birth cohort conducted in Madang Province, Papua New Guinea, designed to develop a fetal weight reference chart for rural Melanesian pregnancies with low risk of growth complications. A total of 439 women, aged 16 to 42 years, with singleton pregnancies were recruited between 2009 and 2013 from six rural health facilities, based on gestational age under 25 weeks. Of these, 376 women had birth weights recorded for their newborns within 24 hours of delivery, forming a birth cohort of mothers and infants. Participants were followed up as many as three times during pregnancy through ultrasound scans at enrollment, late second trimester, and mid-third trimester, with an average interval of 69 days between scans.